In many machining operations, an aquaeous coolant is sprayed or flowed at the location where a cutting tool engages the workpiece, for lubrication and cooling purposes. The coolant is then collected in a tank located below the machine and recycled for continuous use for as long as possible.
Aquaeous coolants of this type are fairly expensive, so it is advantageous to maintain such aquaeous coolants in usable condition for as long as possible. Typical machining operations also include lubricating oil for lubricating movable parts. Eventually, this oil drips or flows into the aquaeous coolant tank, where it floats upon the surface of the aquaeous coolant due to its lighter weight and lower density. This oil, referred to as "tramp oil," will eventually also contribute to bacterial growth within the aquaeous coolant, resulting in a foul odor and reducing the useful life of the aquaeous coolant.
Due to environmental concerns, the oil-contaminated aquaeous coolant must be treated as hazardous waste, and therefore represents an environmental and economic concern. Thus, tramp oil represents a serious environmental and economic problem with respect to maintaining proper and cost effective aquaeous coolant use during machining operations.
A number of skimming devices have been developed over the years to remove tramp oil from the surface of aquaeous coolant in a coolant tank for a machine. Disk skimmers include a disk which extends into the aquaeous coolant and into contact with the tramp oil. Rotation of the disk near the surface results in removal of some oil from the surface, whereupon it is scraped by a blade and removed. Belt type skimmers involve an endless belt which removes tramp oil from the surface of the aquaeous coolant, whereupon it is also scraped therefrom for removal. Disk and belt skimmers of this type are relatively inefficient and have space limitations for proper mounting and operation.
Floating tube skimmers and weir-type skimmers adapt to liquid level fluctuations, and they generally include a pump for pumping the skimmed liquid to a separation device. Such skimmers have proved to be acceptable in relatively large bodies such as lakes, ponds, rivers or even oceans. However, their size typically prevents their use in machining applications. In machining operations, most coolant tanks are as shallow as five or six inches, or as deep as 14 to 16 inches. Also, some machining coolant tanks are located in relatively inaccessible places without much spare space located adjacent thereto.
Weir-type skimmers also have the disadvantage of being too large to be readily adapted for machining operations. With floating tube or weir-type skimmers, liquid is retrieved from the tank via a suction line operatively connected to a suction pump. For most operations of this type, a positive displacement pump provides this suction force. Because the liquid removed from the tank includes a mixture of two different liquid components, and the proportions of these two liquid components vary over a period of use, the volume pulled by the pump is subject to variation. These volume variations can adversely affect the efficient operation of the pump and the entire system. Thus, while these relatively large size skimming devices have proved effective in their specific environment, i.e. large bodies of water, they suffer from some disadvantages which would be aggravated if the devices were to be adapted for use in relatively small coolant tanks.
In summary, in machining operations it is necessary to skim primarily tramp oil from the surface of the aquaeous coolant in the tank (though the skimmed liquid will also include some coolant), to deliver the tramp oil coolant mixture to a separation unit, to separate the tramp oil from the aquaeous coolant for collection, and to return the aquaeous coolant to the tank for reuse.
It is an object of this invention to optimize the useful life of aquaeous coolant used in conjunction with the operation of a machine tool. As a corollary, it is also an object of this invention to minimize the bacteria formation and hazardous waste conditions created by tramp oil contamination of such aquaeous coolant.
It is another object of this invention to improve the skimming efficiency of an aquaeous coolant skimmer, for varying liquid levels in the tank.
It is still another object of the invention to maintain consistency in liquid flow from a skimmer to a coalescer, thereby to optimize the useful life of the pump which causes the flow and to minimize the possibility of damage to the pump.
It is still another object of the invention to achieve the above-noted objects for a variety of differently sized and shaped tanks for collecting and holding aquaeous coolant.